Runflat tire with fabric underlay and tread insert

ABSTRACT

A pneumatic radial ply tire ( 50 ) having a tread ( 52 ), a carcass ( 60 ) with two sidewalls ( 77, 78 ), one or more radial plies ( 70, 72 ), two annular beads ( 36   a   ′, 36   b ′), a belt structure ( 56 ) located radially between the tread and the radial ply structure ( 58 ), a fabric underlay ( 54 ), deployed radially inward of the belt structure, and a tread insert ( 66 ) deployed between the belt structure and the fabric underlay. Said underlay ( 66 ) contains circumferentially aligned high-modulus fibers or cords ( 88 ) which, in combination with metal belt structure ( 56 ) and the tread insert ( 66 ), contribute to circumferential tread rigidity. Insert ( 66 ), in conjunction with the belt structure ( 56 ) and the radial ply structure ( 58 ), contributes to lateral tread rigidity. The circumferential and lateral stiffening of the tread ( 52 ) enhances high-speed runflat handling and contributes to improved runflat operational life.

TECHNICAL FIELD

The present invention relates to a pneumatic radial ply runflat tirewhose runflat handling is improved by providing a means for stiffeningthe tread and its underlying support structure. The increased rigidityimproves the tire's runflat capability by resisting the tendency of thecenter of the tread to buckle upward during operation under conditionsof unpressurized or underpressurized operation. During high-speedoperation, the increased rigidity resists upward buckling of the centerpart of the tread and its underlying structure thereby enhancing thetread's ground contact and lateral grip.

BACKGROUND OF THE INVENTION

Various methods have been devised for enabling the safe, continuedoperation of unpressurized or underpressurized vehicle tires with theintent of minimizing further damage to the uninflated tire and withoutsimultaneously compromising vehicle handling over a distance from theplace where the tire lost its pressure to a place desired by the driver,such as a service station where the tire can be changed. Loss of tirepressure can result from a variety of causes, including puncture by aforeign object such as a nail or other sharp object piercing thepneumatic tire installed on a vehicle.

Pneumatic tires designed for sustained operation under conditions ofunpressurization or underpressurization are also called runflat tires,as they are capable of being driven in the uninflated or “flat”condition. The conventional pneumatic tire, when operated withoutinflation, collapses upon itself, its sidewalls buckling outward in theregion where the tread contacts the ground, when supporting a vehicleload. In general, the term “runflat” means that the tire structure alonehas sufficient rigidity and strength to support the vehicle load whenthe tire is operated in the uninflated condition such that the sidewalland internal surfaces of the tire do not collapse or buckle ontothemselves, i.e., without recourse to incorporation of other internalsupporting structures and devices to prevent the tire from collapsing.

An example of a runflat tire design is described in U.S. Pat. No.4,111,249, entitled the “Banded Tire,” in which a hoop or annular bandapproximately as wide as the tread is circumferentially deployed beneaththe tread. The hoop in combination with the rest of the tire structurecould support the vehicle weight in the uninflated condition. This priorart banded tire is disclosed as being able to actually induce tensionthe ply cords even in the uninflated condition.

Numerous methods have been used to achieve workable runflat tiredesigns. Generally, such tires incorporate sidewall designs that arethicker and/or stiffer, so that the tire's load can be carried by anuninflated tire with minimum adverse effects upon the tire itself andupon vehicle handling until such reasonable time as the tire can berepaired or replaced. The methods used in sidewall stiffening includethe incorporation of circumferentially disposed inserts in the innerperipheral surface of the sidewall portion of the carcass, which is theregion in the tire usually having the lowest resistance to deformationunder vertical loading. In such runflat tire designs, the thickness ofthe sidewalls increases and decreases again to form a crescent shapedsection between the bead and the tread. The reinforced sidewalls of suchtires, when operated in the uninflated condition, experience a netcompressive load. The outer portions of the reinforced sidewalls are intension due to bending deformation which deflects the sidewalls outwardor apart from one another in the regions of the sidewall adjacent to theground-contacting portion of the tread. The inner portions of suchreinforced sidewalls, in the region near where the tread contacts theground, tend to be in compression during runflat operation.

Due to the large amounts of rubber required to stiffen the sidewallmembers, heat buildup due to flexure of the sidewalls is a major factorin tire failure, especially when the uninflated tire is operated forprolonged periods at high speeds.

A Goodyear patent, U.S. Pat. No. 5,368,082 ('082) disclosed a low aspectrunflat pneumatic radial ply tire, which employs special sidewallinserts to improve stiffness. Approximately six additional pounds (2.72kilograms) of weight per tire was required to support 800 pounds (lb.)[360 kilograms] with this uninflated tire.

This earlier invention, although superior to prior attempts at runflattire design, still imposed a weight penalty that could be offset by theelimination of a spare tire and the tire jack. However, this weightpenalty was even more problematic when the engineers attempted to buildhigh-aspect-ratio tires for large luxury touring sedans. These tallersidewalled tires, having aspect ratios in the 55% to 65% range orgreater, means that the sidewall bending stresses are greater than thatof the earlier low-aspect-ratio runflat tires disclosed in the '082patent. Thus the sidewalls of high profile tires had to be stiffened tothe point of compromising ride characteristics. Luxury vehicle ownersgenerally do not wish to sacrifice ride quality for runflat capability.The engineering requirements for runflat tire design require that therebe no loss in ride or performance. In the very stiff suspensionperformance type vehicle, such as sport cars and various sport/utilityvehicles, the ability to provide such runflat tires is relativelystraightforward compared to providing similar runflat tires for luxurysedans which require softer ride characteristics. Light trucks and sportutility vehicles, although not as sensitive to ride performance, providea runflat tire market that ranges from accepting a stiffer ride todemanding the softer luxury type ride.

French Patent Application 78 13956, Publication No. 2,245,334, disclosesa tire having a pair of reinforcing plies 23.2, a lower reinforcing ply31, an intermediate layer of rubber 30 and a lenticular section 20contained in each “wall 14”. U.S. Pat. No. 4,262,726 discloses a tirehaving a soft rubber cushion 29 between a carcass overlay 20 and anearest belt ply 15, to permit unhampered reorientation of the cords ofthese two components during molding.

In general, runflat tire design is based on the installation of one ormore inserts inside each sidewall flex area. The inserts in eachsidewall, in combination with the plies, add rigidity to the sidewallsin the absence of air pressure during runflat operation. While the highresistance to compression deflection of the inserts provides thenecessary resistance to the collapse of the uninflated loaded tire, thismethod has several drawbacks which include the above mentioned increasein tire weight and, especially during runflat operation, heat buildup inthe insert reinforcements of the sidewalls.

Moreover, during runflat operation, the thick reinforced sidewalls tendto transmit bending stresses to the portion of the tread that contactsthe ground. The result is that the central portion of the tread tends tobuckle upwards from the ground. The upward buckle reduces the groundcontact in the tread's central region, resulting in compromised vehiclehandling as well as reduced runflat tread life.

Upward buckling of the tread has adverse effects upon vehicle handlingin the runflat mode. Also, the cyclical flexure of the tread duringrunflat operation tends to cause excessive heating of the treadmaterial, especially during high-speed operation. The excessive heatingleads to deterioration of the tire structure in the region of the treadand thereby reduces the runflat tire's operating life in the runflatmode. A hypothetically perfect runflat tire would be able to maintainthe central portion of its tread in the same degree of road contactduring runflat operation as during fully inflated operation. Then, thehigh speed handling of the tire would be improved because of theincreased lateral grip of the tire.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a runflat radialtire as defined in one or more of the appended claims and, as such,having the capability of being constructed to accomplish one or more ofthe following subsidiary objects.

One object of the present invention is to provide a runflat radial tirehaving a laterally stiffened tread that resists upward buckling duringrunflat operation.

Another object of the present invention is to provide a runflat radialtire having a circumferentially stiffened tread that resists upwardbuckling during runflat operation.

Still another object of the present invention is to provide a runflatradial tire having good high-speed runflat handling characteristics byemploying lateral and circumferential stiffening of the tread so as toresist buckling, and consequent loss of ground contact, during runflatoperation.

Yet another object of the present invention is to provide a runflatradial tire having good runflat service life as a result of reducedflexure of the tread during runflat operation.

SUMMARY OF THE INVENTION

The present invention relates to a pneumatic radial ply runflat tirehaving a tread, a casing with two insertreinforced sidewalls, twoinextensible annular beads, a radial ply structure, a belt structurelocated radially between the tread and the radial ply structure, afabric underlay characterized by being deployed radially inward of thebelt structure and radially outward of the radial ply structure, and anelastomer insert characterized by being circumferentially deployedradially inward of the belt structure and radially outward of the fabricunderlay and the underlying radial plies. The high-modulus reinforcingcords of the fabric underlay are circumferentially aligned, and they arecapable of supporting tensile loads. The elastomeric insert, locatedbeneath the belt structure, extends across about 40 percent to about 100percent and preferably about 50 percent to about 90 percent of the widthof the belt structure and is centered upon the tire's equatorial plane.The insert acts to separate the belt structure from the fabric underlayand the radial ply structures, thereby giving mechanical advantage tothe compression-load-bearing belt structure which, in concert with thefabric underlay, contributes to the tread's circumferential rigidity,the insert, also acting in concert with the radial ply structure,contributes to the tread's lateral rigidity. At least one of the radialplies might be reinforced with inextensible metal cords.

In one embodiment of the invention, the pneumatic runflat radial tirehas low-aspect-ratio (in the range of about 30% to about 60%) design.Such an embodiment has potential for runflat use in high-performancesports type vehicles or light trucks. This low-aspect-ratio, radial ply,runflat pneumatic tire contains two radial belts, a fabric underlaydeployed circumferentially about the tire, radially outward of the plystructure and radially inward of the belt structure, and an elastomericinsert circumferentially deployed radially inward of the belt structureand radially outward of the fabric underlay. The fabric underlay hasreinforcing cords that are oriented circumferentially, more or lessparallel to the tire's equatorial axis. The combination of the insertand the tensile-stress-bearing fabric underlay contributes tocircumferential rigidity of the tread, and the combination of the insertand the radial plies contributes to lateral rigidity of the tread. Theenhanced rigidity of the tread resists upward buckling of the centralportion of the tread during runflat operation, thereby maintaining goodtread-to-road contact and providing improved high-speed runflat vehiclehandling. The enhanced rigidity of the tread also reduces the runflatcyclical flexure that can cause heat buildup and consequent tiredeterioration.

A second embodiment of this invention relates to a high-aspect-ratio (inthe range of about 50% to about 80%) version for a high-profile tire. Anexample of a use of the high-profile embodiment would be in luxury-typevehicles, high-standing sport-utility vehicles, and some light trucks.During runflat operation of the second embodiment, the enhanced lateraland circumferential rigidity of the tread contributes improved runflathandling and stability as well as a longer runflat service life.

A third embodiment of this invention relates to a radial ply runflattire having at least one radial ply which is reinforced by essentiallyinextensible cords, such as steel, and in which the aspect ratio of thetire can be between the maximum and minimum values of aspect ratios forrunflat tires (in the range of about 30% to about 80%).

A fourth embodiment of this invention relates to a radial ply runflattire having a fabric overlay deployed radially outward of the beltstructure in conjunction with the fabric underlay of the firstembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the invention will becomefurther apparent upon consideration of the following description takenin conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a prior art runflat tire designincorporating insert-reinforced sidewalls;

FIG. 2a is a cross-sectional schematic view of a section of theground-contacting portion of the prior art runflat tire of FIG. 1 innormally inflated condition;

FIG. 2b is a cross-sectional schematic view a section of theground-contacting portion of the prior art runflat tire of FIG. 1 in anuninflated condition;

FIG. 3 is an enlarged fragmentary schematic cross-sectional view of theupward-buckled central portion of the uninflated, prior art runflat tireshown in FIG. 2b;

FIG. 4 is a cross-sectional view of a pneumatic, radial ply, runflattire incorporating the features of the present invention;

FIG. 5 is a schematic, cross-sectional diagram showing the operativeelements of the tread-reinforcing components of the present invention;

FIG. 6 shows a centrally loaded I-beam, for explaining the operation ofthe inventive concept of the present invention;

FIG. 7a is a schematic view of the fabric underlay of the presentinvention and the orientation of its reinforcing cords;

FIG. 7b shows the orientation with, respect to the tire's equatorialplane, of the one of the reinforcing cords of the fabric underlay shownin FIG. 7a; and

FIG. 8 is a cross-sectional view of a pneumatic, radial runflat tire inaccordance with a second embodiment of the present invention whichincorporates a fabric underlay in conjunction with a fabric overlay.

DEFINITIONS

“Apex” means an elastomeric filler located radially above the bead coreand between the plies and the turnup plies.

“Aspect ratio” means the ratio of the section height of a tire to itssection width.

“Axial” and “axially” means the lines or directions that are parallel tothe axis of rotation of the tire.

“Bead” or “Bead Core” generally means that part of the tire comprisingan annular tensile member of radially inner beads that are associatedwith holding the tire to the rim; the beads being wrapped by ply cordsand shaped, with or without other reinforcement elements such asflippers, chippers, apexes or fillers, toe guards and chafers.

“Belt Structure” or “Reinforcement Belts” means at least two annularlayers or plies of parallel cords, woven or unwoven, underlying thetread, unanchored to the bead, and having both left and right cordangles in the range from 18° to 30° relative to the equatorial plane ofthe tire.

“Breakers” or “tire breakers” means the same as belt or belt structureor reinforcement belts.

“Carcass” means the tire structure apart from the belt structure, tread,undertread over the plies, but including the beads.

“Casing” means the carcass, belt structure, beads, sidewalls and allother components of the tire excepting the tread and undertread.

“Circumferential” most often means circular lines or directionsextending along the perimeter of the surface of the annular treadperpendicular to the axial direction; it can also refer to the directionof the sets of adjacent circular curves whose radii define the axialcurvature of the tread, as viewed in cross section.

“Cord” means one of the reinforcement strands, including fibers, withwhich the plies and belts are reinforced.

“Crown” or “Tire Crown” means the tread, tread shoulders and theimmediately adjacent portions of the sidewalls.

“Equatorial plane” means the plane perpendicular to the tire's axis ofrotation and passing through the center of its tread; or the planecontaining the circumferential centerline of the tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Innerliner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“Insert” means the crescent- or wedge-shaped reinforcement typicallyused to reinforce the sidewalls of runflat-type tires; it also refers tothe elastomeric, non-crescent-shaped insert that underlies the tread.

“Lateral” means a direction parallel to the axial direction.

“Normal Inflation Pressure” means the specific design inflation pressureat a specified load assigned by the appropriate standards organizationfor the service condition for the tire.

“Normal Load” means the specific design load at a specified inflationpressure assigned by the appropriate standards organization for theservice condition for the tire.

“Ply” means a cord-reinforced layer of rubber-coated radially deployedor otherwise parallel cords.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Radial ply structure” means the one or more carcass plies or which atleast one ply has reinforcing cords oriented at an angle of between 65°and 90′ with respect to the equatorial plane of the tire.

“Radial ply tire” means a belted or circumferentially-restrictedpneumatic tire in which at least one ply has cords which extend frombead to bead and are laid at cord angles between 65° and 90° withrespect to the equatorial plane of the tire.

“Section Height” means the radial distance from the nominal rim diameterto the outer diameter of the tire at its equatorial plane.

“Section Width” means the maximum linear distance parallel to the axisof the tire and between the exterior of its sidewalls when and after ithas been inflated at normal pressure for 24 hours, but unloaded,excluding elevations of the sidewalls due to labeling, decoration orprotective bands.

“Shoulder” means the upper portion of sidewall just below the treadedge.

“Sidewall” means that portion of a tire between the tread and the bead.

“Tangential” and “tangentially” refer to segments of circular curvesthat intersect at a point through which can be drawn a single line thatis mutually tangential to both circular segments.

“Tread contour” means the shape of a tire tread as viewed in axial crosssection.

“Tread width” means the arc length of the tread surface in the planeincludes the axis of rotation of the tire.

“Wedge insert” means the same as “insert.”

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Prior Art Embodiment

With reference to FIG. 1, a cross section of a typical prior art,low-profile pneumatic radial runflat tire 10 is illustrated. The tire 10has a tread 12, a belt structure 14, a pair of sidewall portions 16,18,a pair of bead regions 20 a and 20 b and a carcass structure 22. Beltstructure 14 consists of two belts 24,26 and a fabric overlay 28deployed between the bottom portion of tread 12 and the upper parts ofthe belt structure. The carcass 22 includes a first ply 30 and secondply 32, a gas-impervious inner liner 34, a pair of beads 36 a, 36 b, apair of bead filler apexes 38 a, 38 b, a first pair of inserts 40 a, 40b and a second pair of inserts 42 a, 42 b. The first or innermost insert40 a, 40 b is located between the inner liner 34 and the first ply 30,and the second insert 42 a, 42 b is located between the first ply 30 andsecond ply 32. Fabric overlay 28 is disposed beneath, or radially inwardof, tread 12 and on top of, or radially outward from, belt structure 14.The reinforced sidewall portions 16,18 of carcass structure 22 give thetire 10 a limited runflat capability.

As can be seen from FIG. 1, the structural reinforcement in the sidewallarea of the tire 10 gives a crescent shaped section to the sidewallportions 16,18. This generalized prior art runflat tire design shows themore or less uniformly thickened sidewalls that characterize runflattire designs. Such insert-reinforced sidewalls are necessary to supportthe tire's load with minimal sidewall deformation when the tire 10 is inan uninflated state. Such runflat tire designs provide reasonablevehicle handling and performance under conditions of full inflation, andthey yield reasonable runflat tire life and vehicle handling when thetire is uninflated. Runflat tires generally weigh more than equivalentnon-runflat-capable tires, because of the additional weight of thereinforcement material in the sidewalls; this additional weight isgreater in highprofile runflat tires than in low-profile runflat tires.

FIG. 2a shows a fragmentary schematic of a normally inflated, prior artrunflat tire 10 with its tread 12 in contact with the ground 13. Theflattening of the tread 12, in the region where it contacts the ground13, induces bending stresses in the tread and its underlying components,including belt structure 14, overlay fabric 28, belts 24,26, radialplies 30,32, and inner liner 34. More specifically, the bending stressesderive from the flattening of the tread 12 from the as-molded andas-inflated lateral curvature of tread and its underlying structures.These bending stresses induce tensile stresses in the radially inwardstructures beneath tread 12, such as the inner liner 34 and the radialplies 30,32.

Corresponding compressive stresses are concurrently induced in theelastomeric material of tread 12 and such underlying structures as thefabric overlay 28 and portions of the belt structure 14.

FIG. 2b illustrates the upward buckling of tread 12 of the uninflated,prior art runflat tire 10 in the region where the load-bearing treadcontacts the flat road surface 13. The upward buckling of the centraltread region corresponds to the formation of bending stresses in thecentral portions of tread 12 and its underlying structures. The bendingstresses in the tread 12 during runflat operation, as illustrated inFIG. 2b are greater than those associated with simple flattening of thetread during normal-inflated operation, as illustrated in FIG. 2a.

FIG. 3 is a fragmentary schematic detail (not in exact proportion) ofthe belts 24,26, plies 30,32, inner liner 34 and fabric overlay 28 asthey would appear within the upward-buckled central portion of the tread12 of the prior art tire of FIG. 2b. The neutral bending axis A—A shownin FIG. 3 is shown located in a plausible relationship with respect tothe fabric overlay 28, belts 24,26, plies 30,32 and inner liner 34.Those skilled in the art will appreciate that, in FIG. 3, the structuralelements of tread 12 which lie above the neutral axis A—A—i.e., radiallyinward of the tread 12—will experience compressive loading, while thosestructures located below the neutral axis A—A, i.e. closer to innerliner 34 will experience tensile loading. The location of neutral axisA—A in relation to belts 24,26 is approximate, taking into account thetensile-stress-bearing capabilities of radial plies 30,32 and thecompressive-stress-bearing capabilities of the belts 24,26. The fabricoverlay 28 is not a compressive-load-bearing structure, nor is the innerliner 34 an effective tensile-load-bearing structure. The neutral axisA—A is shown to be located within belt 24 purely as an approximation ofwhere it would lie given the relative greater modulus of elasticity ofthe steel cords in belts 24,26 compared to the modulus of the cords thatreinforce the plies 30,32. It is recognized that greater or lesserdegrees of upward buckling of the central portions of the tread, asillustrated in FIGS. 2b and 3, plausibly will cause the location to theneutral bending axis A—A to change correspondingly with regard to theradial direction.

FIG. 4 shows runflat tire 50 according to the present invention. Tire 50has the same general sidewall construction as that of the prior artrunflat tire 10 shown in FIG. 1. One of the inventive features of tire50 in FIG. 4 is a fabric underlay 54 deployed between the belt structure56 and the radial ply structure 58 of carcass structure 60. Fabricunderlay 54 has lateral margins 62,64, which lie beyond the lateraledges of the belt structure 56. The reinforcing cords of fabric underlay54, as shown in FIGS. 7a and 7 b, are oriented in the range of 0 toabout 10 degrees with respect to the tire's equatorial plane, with thepreferred orientation being between about 0 and about 5 degrees.

A second inventive feature, as shown in FIG. 4, is a circumferentiallydeployed wedge insert 66 deployed between the radially inward belt 67 ofbelt structure 56 and the fabric underlay 54. The insert 66 islenticular in cross-section. The lateral, or axial, width of insert 66is from about 50 percent to about 90 percent of the lateral width oftread 52. The maximum thickness of the insert 66 occurs at thecentral-most portion of the tread, i.e., at the tire's equatorial planeEP, which is shown as centerline CL in FIG. 4. Typically, in a runflattire of the present invention the thickness of the insert 66 is betweenabout 1 and 8 millimeters and preferably between about 2 and 5millimeters. Insert 66 is made of a low hysteresis elastomer compoundhaving a hardness of about 60 to about 90, and preferably between about70 to about 80, and most preferably about 75 on the Shore A scale.

FIG. 5 is a fragmentary, schematic cross-sectional view of tire 50showing the insert 66 in locational relationship to tread 52, the beltstructure 56 (comprising inner belt 67 and outer belt 68), fabricunderlay 54, radial ply structure 58 (comprising inner ply 70 and outerply 72) and inserts 42 a′ and 42 b′. Throughout the specification,primed numbers represent structural elements which are substantiallyidentical to structural elements represented by the same unprimednumber. The practice of the inventive concept will become evident in thedescription below.

Tread Insert

Referring to FIGS. 4 and 5, tread insert 66 can be seen to act as aseparator between the belt structure 56 and the combination of thefabric underlay 54 and the radial ply structure 58. The separator effectof insert 66 is equivalent to the separator effect of the web portion ofa standard structural steel “I” beam consisting of two “flanges”separated by a single “web,” as illustrated in FIG. 6.

FIG. 6 shows an I-beam segment 80, supported at its ends by supports Aand B. I-beam 80 is shown supporting a central load L. In FIG. 6, theload L is such that the upper flange 82 of I-beam 80 is in compression,while the lower flange 84 is in tension. Flanges 82,84 are separatedfrom one another by web 86. Assuming that the dimensions and physicalproperties of flanges 82,84 are the same, and that the thickness of theweb 86 is uniform between the flanges, then the neutral bending axis A—Awill be located at the center of the I-beam 80, as shown in FIG. 6. Asthe width W of web 86 increases, the moment of inertia of beam 80correspondingly increases with respect to bending under the force ofload L. In other words, the rigidity of the I-beam 80, with respect todeformation under the weight of load L, increases in direct relation tothe width of web 86, as it separates flanges 82,84. Similarly, in FIGS.4 and 5, insert 66 operates in a similar fashion to that of web 86 inFIG. 6; i.e., insert 66 separates the belt structure 56 from the plystructure 58, each of which, respectively, is equivalent in respectivecompressive- and tensile-load bearing capacity to the flanges 82,84 ofI-beam 80 in FIG. 6.

Referring now to FIGS. 4 and 5, it should be evident that under runflatconditions, the tendency of the central portions of tread 52, andadjacent underlying structures, to buckle upwards in the region of thecenterline CL will induce compression stresses in the steel beltstructure 56 and tensile stresses in the radial ply structure 58. Thoseknowledgeable in the art will understand that the thickness of insert 66enhances the respective mechanical advantages to the compression-loadedbelt structure 56 and tensile-loaded radial ply structure 58 such thatthe overall system of the belt structure, the ply structure, and insert66 will have greater resistance to upward buckling of the tread 52 underrunflat conditions. In other words, as illustrated in the I-beam exampleshown in FIG. 6, the compression-bearing flange 82 is equivalent to, orcorresponds to, the belt structure 56 in FIGS. 4 and 5, whiletension-bearing flange 84 is equivalent, or corresponds to, the radialply structure 58; also the web 86 in FIG. 6 is equivalent to, orcorresponds to, the insert 66. Insert 66 separates the respectivecompression-loaded belt structure 56 from the tensile-loaded radial plystructure 58, thereby enhancing the lateral rigidity of tread 52 withrespect to upward buckling during runflat operation.

Underlay

The fabric underlay 54 shown in FIG. 4 is reinforced with high moduluscords made of materials selected from the group that includes aramid,polyester, rayon and glass. FIG. 7a is an edge-on view of tire 50; thetread and belt structure are not shown in FIG. 7a so that theorientation of the underlying reinforcing cords 88 of the fabricunderlay 54 can be illustrated in their approximately circumferentialorientation. FIG. 7b is detail view showing the orientation ofreinforcing cords 88 in relation to the equatorial plane EP. The rangeof angles between the cords 88 and the equatorial plane EP is between 0and about 10 degrees, with between 0 to about 5 degrees being thepreferred range of orientation.

The orientation of the high-modulus cords 88 in the fabric underlay 54is such that, as those skilled in the art will recognize, thereinforcing cords will contribute resistance to tensile-stress-inducedcircumferential deformation. Furthermore, because fabric underlay 54 islocated radially inward of insert 66, i.e., between the insert and theradial ply structure 58, the reinforcing cords 88 of the fabric underlaywork in concert with the insert and the belt structure 56 to contributecircumferential rigidity to the tread. In other words, referring to FIG.6, the compression-bearing flange 82 is equivalent to the belt structure56 in FIGS. 4 and 5, while tension-bearing flange 84 is equivalent tothe fabric underlay 54, and web 86 is equivalent to insert 66 whichseparates the respective compression-loaded belt structure from thetensile-loaded circumferential cords of the fabric underlay, therebyenhancing the tread's circumferential rigidity with respect to upwardbuckling during runflat operation.

Operation of the Inventive Concept in Relation to Prior Art

The inventive concept addresses the tread buckling associated withrunflat tires when they are operated in the runflat mode.

To reiterate the origins of the tread buckling (which is also known as“tread lift”) associated with runflat operation of runflat-type tires,the reinforced sidewalls of a prior art uninflated runflat tire 10 ofthe type shown in FIG. 1 tend to buckle axially outwards in such a wayas to transmit upward-directed bending stresses to the tire's tread 12and underlying structures such that the central portion of the treadundergoes reduced to zero contact with the road. Upward buckling of thetread can have adverse effects upon vehicle handling in the runflatmode, especially during high-speed operation. In addition, the cyclicalflexuring of the tread during runflat operation tends to cause heatingof the tread material, especially during high-speed operation, which cancause deterioration of the tire structure in the region of the tread,thereby reducing the runflat tire's operating life in the runflat mode.A hypothetically perfect runflat tire would be able to maintain thecentral portion of its tread in the same degree of road contact duringrunflat operation as during fully inflated operation.

In this invention, the incorporation of the wedge insert 66 radiallyinward of the belt structure 56 and radially outward of the radial plystructure 58 and the fabric underlay 54 increases the tread's rigidityin the lateral direction and in the circumferential direction.

Dynamic Operation of Preferred Embodiment

The operation of wedge insert 66 of the present invention, as shown incross-sectional view in FIG. 4, is such as to separate the beltstructure 56 from the combination of the fabric underlay 54 and theradial ply structure 58. During runflat operation of tire 50, the beltstructure 56 experiences compressive loading in response to the tendencyof the central portion of tread 52 to lift away from, or buckle upwardfrom, the ground 13, as shown in FIG. 2b. At the same time, the radiallyoriented reinforcing cords of the radial ply structure 58 experiencetensile loading. Insert 66, by separating the compression-load-bearingbelt structure 56 from the tension-load-bearing radially oriented cordsof radial ply structure 58, acts in a way that is equivalent to that ofthe web of a structural steel I-beam, thereby contributing to thelateral rigidity of the tread 52 and its underlying structures.

With regard to the operation of wedge insert 66 in relation to thefabric underlay 54, as shown in FIG. 4, the insert separates the beltstructure 56 from the fabric underlay 54 with its circumferentiallyoriented reinforcing cords 88. During runflat operation, the beltstructure 56 experiences compressive loading in response to the tendencyof the central portion of tread 52 to lift away from the ground. Underthe same runflat conditions, the circumferentially oriented reinforcingcords of the fabric underlay 54 experience tensile loading. Insert 66,by separating the compression-load-bearing belt structure 56 from thetension-load-bearing circumferentially oriented cords 88 of the fabricunderlay 54, acts in a way that is equivalent to that of the web of astructural steel I-beam, thereby contributing to the circumferentialrigidity of the tread 52 and its underlying belts, plies and otherstructures.

Thus it follows that the compression-load-bearing capacity of the beltstructure 56, in combination with the tensile-load-bearing capacity ofthe radially reinforced ply structure 58 and the circumfenentiallyreinforced fabric underlay 54, result in a runflat tire design havingboth lateral and circumferential enhanced resistance to upward bucklingof the tread during runflat operation. One immediate benefit of suchenhanced tread rigidity is improved tread contact with the road andthereby improved vehicle handling during runflat operation, especiallyat high speeds. Another benefit is enhanced runflat tire life resultingfrom a reduction in the amount of cyclical tread flexure, especiallyduring high-speed driving. I.e., severe tread flexure results in heatbuildup which can cause deterioration of the tire structure duringrunflat operation. This invention, by increasing both lateral andcircumferential tread rigidity, reduces the amount of tread flexure andsubsequent heat build up, thereby giving an improved runflat tire life.

EMBODIMENT ONE

Referring to FIG. 4, there is illustrated a first embodiment of theinvention wherein the runflat radial ply tire 50 has a low-aspect-ratiodesign in the range of about 30 to about 60%. Such an embodiment wouldhave potential for runflat use in high-performance sports type vehiclesor light trucks. This low-aspect-ratio runflat radial ply runflatpneumatic tire 50 contains two belts 67,68, a fabric underlay 54, and atread insert 66. Fabric underlay 54 has reinforcing cords 88 that areoriented circumferentially around the tire, more or less parallel to thetread centerline and perpendicular to the tire's axis of rotation. Treadinsert 66 acts as a separator between the respective compressive-loadbearing belt structure 56 and the respective lateral tension-bearingcords of the radial ply structure 58 and the circumferentialtension-bearing cords 88 of the fabric underlay 54. During runflatoperation, the improved lateral and circumferential rigidity of thetread contributes better vehicle handling and stability duringhigh-speed runflat operation. The improved lateral and circumferentialrigidity also acts to decrease the flexure which, during runflatoperation, can cause heat build up that can accelerate the deteriorationof the tire.

EMBODIMENT TWO

A second embodiment of this invention is envisioned in which ahigh-aspect-ratio version of the runflat radial ply tire 50, shown inFIG. 4, has a high aspect ratio design in the range of about 50 to about80%. An example of a use of the high-aspect ratio runflat radial plytire would be in luxury-type vehicles, high-standing sport-utilityvehicles, and some light trucks. As with EMBODIMENT ONE, the improvedlateral and circumferential rigidity of the tread contributes betterrunflat tire life and better vehicle handling and stability duringhigh-speed runflat operation.

EMBODIMENT THREE

A third embodiment is envisioned in which this invention is incorporatedwithin a radial ply runflat tire, as also shown in FIG. 4, having atleast one radial ply 70 or 72 which is reinforced by essentiallyinextensible fibers or cords made of metal such as steel, such asdisclosed in U.S. Pat. No. 5,871,600, which is incorporated by referencein its entirety herein, and in which the aspect ratio of the tire can below or high or intermediate between the maximum and minimum values ofaspect ratios for runflat tires.

EMBODIMENT FOUR

A fourth embodiment, as shown in FIG. 8, is envisioned in which thisinvention is incorporated within a radial ply runflat tire 150 having afabric overlay 55, similar to fabric overlay 28 of FIG. 1, used inconjunction with fabric underlay 54′ and the wedge insert 661. Theoverlay 55, extends over the ends of the underlay 54′ and beneath, orradially inward of, tread 12 and on top of, or radially outward from,belt structure 14′. The other structural elements of tire 150 aresubstantially identical with those in tire 50 shown in FIG. 4, asdiscussed before.

Accordingly, the present invention as disclosed herein includes arunflat radial tire having both a laterally and a circumferentiallystiffened tread that resists upward buckling during runflat operation aswell as provide good high-speed runflat handling because of theresistance to loss of ground contact during runflat operation. Inaddition the runflat service life is increased as a result of reducedflexure of the tread during runflat operation.

While the invention has been described in combination with embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing teachings. Accordingly, the invention is intended to embraceall such alternatives, modifications and variations as fall within thescope of the appended claims.

What is claimed:
 1. A pneumatic radial ply runflat tire (50) having atread (52), a belt structure (56), two beads (36 a,36 b) two sidewalls(77,78), an inextensible ply structure (58) and an underlay (54) betweenthe belt structure and the ply structure; each sidewall having one ormore sidewall inserts (40 a,40 b,42 a,42 b), the runflat tirecharacterized by: the underlay (54) being a fabric underlay, disposedbetween the belt structure and the ply structure, and centered around anequatorial plane (CL) of the tire and having high modulus reinforcingcords oriented 0 degrees to 5 degrees with respect to the equatorialplane; and the tire having an elastomeric lenticular tread insert (66)circumferentially disposed between the fabric underlay and the beltstructure, the tread insert having a width of 50 percent to 90 percentof the lateral width of tread and a maximum thickness at the equatorialplane.
 2. The tire (50) of claim 1 further characterized by the insert(66) extending about 40% to about 100% of a width of the belt structure(56).
 3. The tire (50) of claim 2, further characterized by the insert(66) extending about 50% to about 90% of the width of the belt structure(56).
 4. The tire (50) of claim 1 further characterized by the insert(66) centered upon an equatorial plane of the tire.
 5. The tire (50) ofclaim 1 in which each sidewall (77,78) contains a single reinforcinginsert.
 6. The tire (50) of claim 1 in which one of the radial plies(70, 72) is reinforced with inextensible metal cords.
 7. The tire (50)of claim 1 having a fabric overlay (55) between the tread (12) and thebelt structure (14′), and extending over the ends of the underlay (54).